There are increasing arguments about family environmental reflection on personality. Living and growing up in a certain environment like a family environment could or could not affects the person personality. This essay will discuss the psychology of how the family environment can affect personality and compare whether siblings in the same family have similarity in personality in order to reach a conclusion of whether family influence leads to similarity in personality or not. Pointing out researches whether sharing genes relates to sharing a personality with twin studies and non-sharing genes with adoptive children, also sharing culture reflect same values within all family members. On the other hand, this essay will converse about how siblings share the same family environment but still very different from each other. From a scientific and genetic perspective, previous research in behavioral genetics has been studied by Psychologist researchers on how genetics and environment can affect personality. In 1991, Hoffman demonstrated that there is a genetic impact on personality, scientists adopted twin studies to find the correlation between identical genes and personality. This study compares monozygotic twins and dizygotic twins in a shared family and a non-shared family. Research had resulted that in the same environment monozygotic twins are more likely to have similar personalities more than the dizygotic twins.A possible explanation for this might be that identical twins genetically share traits and they are more likely to do several activities together and attend same events which lead to more similarity in personality stems from their mutual environment. This study took another perspective to find the differences in personality between monozygotic twins who have been reared apart in different families. In a previous study of Bronfenbrenner (1986), it has been shown that the percentage of similarity among twins reared apart was substantially shrunken. This concludes to that genes can not only define the person’s personality also family environment has a major impact on personality. Another argument which has drawn attention to the family impact on personality is adoption studies. Which studies those who have been adopted after a reasonable time after birth and have been reared by other parents not related to them genetically to see the influence of a shared rearing environment. Psychologists in this field set out a test for genetically unrelated children adopted together in the same family. Results showed that there is a small percentage of similarity this does not mean that family rarely influence personality, the idea is that environmental influence does not work on each family it also has an individual base so even if every person in the family has been affected with a certain event it will not be experienced the same by every individual (Braungart et al., 1992). Another leading factor is siblings sharing the same environmental culture as culture is considered to be an increasingly important pattern in shaping personality.Culture psychology can provide an understanding of how people think and behave from the culture that they are surrounded by and how cultural environment influences them.While siblings are living in the same culture they may share some personality traits and share similar family values. Han and Pöppel(2013)studied the impact of culture on the neuroscience of perception resulting that people who share the same culture matched in their agreement about perceptions of personality diverse and physical traits. On the other hand, it can be noticed that there are many siblings in multi-child families related to each other and share genes, homes, routines, and parents, but have very different personalities and different learning styles, attitudes, motivations and reaction to various things.That is why some people disagree with the theory of sharing family environment could lead to similar personalities. Researchers carried out a research on birth order which is also known as the psychological birth order and how it can affect children personalities. According to Cecile and Jules(1983), it has been remarked that older siblings have different experiences than their later-born siblings because parents usually have more expectation from their firstborn child, as a result, the oldest sibling tends to be more responsible and overrepresented towers their studies and career. Comparatively, the last born tend to have a strong personality and become active but less independent. As Cecile and Jules (1983) stated that youngest children occasionally think that they are indomitable since they get considerable attention from adults around them. As a consequence, they might not see the outcomes of their actions and they are believed to be fearless to do risky things. Furthermore, middle-born are known for their ability in dealing with the different situation around them. Middle-born children usually receive less attention than their oldest and youngest siblings which lead them to search for other relationships somewhere else, consequently, they tend to be social and have great relationships with friends. Another important element for siblings differ in personality is the gender and how do parents deal with each one. As it can be noticed parents interestingly treat their son differently than their daughter, so although these siblings are sharing the same family environment but they still get different treatment which affects their personality in different ways. Maccoby and Jacklin (1974) proved that parents do actually treat their children differently according to their gender. As it is reported by Siegal (1987), fathers usually take the critical role in the family. Moreover, fathers direct their sons to be independent and often impose discipline and control on them, though fathers may promote daughters to be independent as well, daughters are treated more kindly (Siegal, 1987, p.184). The last and the most effective element in personality differences between siblings is the different experiences that each sibling goes through. As stated by Hoffman (1991), there are events happens to a sibling and not the other which consequently lead each person to a different personality direction. There are two types of events which might occur in the child’s life, one is an event for a long period of time such as having an illness, accident or a disability, in these cases the child will have a unique experience than his other siblings and might get different treatment from his parents. In addition, there might be a one-time event occurrence that has a significant impact on the child personality such as listening to a conversation between parents which guide him or her to feel as they are unloved and unwanted. Furthermore, as this essay mention how there are many family experiences, however, There are many external influences which cannot be shared by all family members and these will contribute to different personalities. For instance, friends group, work environment and different experiences which could affect and inspire or change the believes or thoughts of a person. In conclusion, “family environment is not a global variable; rather it is multidimensional” (Hoffman1991, p.199). Sharing same family environment will lead to sharing some %%% but will also differ in many more. If it has been compared between two brothers and two random people, brothers are more likely to have similarity in personality, but this similarity is limited because everyone has a separate life and goes through different situations and different experiences which will differ their personalities depending on each individual and how do he or she take these situations across.